1. Field of the Invention
The present invention relates to a semiconductor integrated circuit formed on a composite semiconductor chip having a compound semiconductor layer on a silicon substrate.
2. Description of the Related Art
To obtain a semiconductor integrated circuit device for a microwave frequency signal, attempts have been made to form a microwave monolithic integrated circuit (MMIC) on a GaAs layer grown on a Si substrate, as disclosed in "IEEE Electron Device Letters", Vol. EDL8, No. 8 (1987), pp. 350-352.
A greater area of the GaAs layer was, however, occupied by input and/or output impedance matching circuit of the GaAs MMIC. Therefore, in order to make the area of the MMIC small, it was necessary to reduce the area occupied by the impedance matching circuit. The area of the impedance matching circuit depends on the thickness of the GaAs/Si wafer (GaAs layer plus Si substrate). Therefore, the thickness of the wafer should be made thinner to reduce the area occupied by the matching circuit.
However, the GaAs/Si wafer used in the "IEEE Electron Device Letters" had a thickness as large as 125 .mu.m, and the area occupied by the MMIC could not be made small.
It would be conceivable to grind the bottom surface of the silicon substrate of the GaAs/Si wafer to reduce its thickness, but the mechanical strength of the wafer requires a thickness in the range of at least 30-50 .mu.m. Thus, a large area is still necessary for the GaAs MMIC. In addition, the film thickness would not become sufficiently uniform through grinding. Consequently, matching of the characteristic impedance would be difficult in the impedance matching circuit, and it would be impossible to obtain excellent high-frequency characteristics.